BEAM FORMING NETWORK

Recently, hearing aid systems where the left and right ear devices collaborate with one another have received much attention. Apart from supporting natural binaural hearing, such systems hold great potential for improving the intelligibility of speech in the presence of noise through beamforming algorithms. Binaural beamforming for hearing aids requires an exchange of microphone signals between the two devices over a wireless link. This paper studies two problems: which signal to transmit from one ear to the other, and at what bit-rate. The first problem is relevant as modern hearing aids usually contain multiple microphones, and the optimal choice for the signal to be transmitted is not obvious. The second problem is relevant as the capacity of the wireless link is limited by stringent power consumption constraints imposed by the limited battery life of hearing aids.

25 SOUND AND VIBRATION/MARCH 2003 bands). It is also important to evaluate the difference between the sound intensity level and the sound pressure level. The descriptor measured in that case is called the PI index. The PI index is equivalent to the mean ...

We report on the further development of our previously described spectroscopic imaging technique based on time-resolved interferometric measurements of laser-induced thermoelastic expansion (POISe: Pulsed Optoelastic Interferometric Spectroscopy and Imaging). We show the capability of POISe to form tomographic images of tissue phantoms and live animal tissues. By performing image reconstruction on data sets acquired from several tissue-like phantoms we demonstrate the ability of POISe to provide better than 200 microns spatial resolution in a strongly scattering medium (μs'=1.5/mm). Additionally we demonstrate the ability of POISe to image chicken chorio-allantoic membrane (CAM) blood vessels through a 6-10 mm layer of Intralipid with μs'=0.75/mm.

Terahertz (THz) transmission is a promising strategy for future 6G networks, offering ultra-wide bandwidth. Effective channel modeling and precoding techniques are essential for achieving required coverage and addressing significant path loss in THz communications. In this paper, we comprehensively examine the major THz precoding algorithms for future 6G networks, focusing on their significant challenges and prospects. We discriminate between millimeter-wave and THz channels and uncover issues with THz precoding, such as distance-dependent direction loss, beam split impact, and excessive power usage. To solve these issues, three distinct THz precoding systems, such as hybrid precoding, analog beamforming, and delay-phase precoding, are introduced and their performance is compared.

Beamforming techniques that employ Singular Value Decomposition (SVD) are commonly used in Multi-Input Multi-Output (MIMO) wireless communication systems. In the absence of channel coding, when a single symbol is transmitted, these systems achieve the full diversity order provided by the channel; whereas when multiple symbols are simultaneously transmitted, this property is lost. When channel coding is employed, full diversity order can be achieved. For example, when Bit-Interleaved Coded Modulation (BICM) is combined with this technique, full diversity order of 𝑵 𝑴 in an 𝑴 × 𝑵 MIMO channel transmitting 𝑺 parallel streams is possible, provided a condition on 𝑺 and the BICM convolutional code rate is satisfied. In this paper, we present constellation precoded multiple beamforming which can achieve the full diversity order both with BICM-coded and uncoded SVD systems. We provide an analytical proof of this property. To reduce the computational complexity of Maximum Likelihood (ML) decoding in this system, we employ Sphere Decoding (SD). We report an SD technique that reduces the computational complexity beyond commonly used approaches to SD. This technique achieves several orders of magnitude reduction in computational complexity not only with respect to conventional ML decoding but also, with respect to conventional SD.

This work presents a new topology of a Coherently Radiating Periodic Structure - Beam Forming Network (CORPS-BFN) and its application for multibeam systems. A unit cell, consisting of a transition from a coaxial input to an intersection of three strip-lines with an angular span of 120 degrees, is proposed and analysed. A periodical replication of the cell gives rise to a uniform layer, allowing a proper matching of the ports of the network. Stacked layers allow in-phase propagation and distribution of the energy through the structure, increasing the number of output ports with each layer.

In this paper, we propose a novel scheme of cooperative relaying network based on data exchange between relays before forwarding their received data to destination. This inter-relay data exchange step is done during an additional middle-slot in order to enhance the transmit signals from relays to the destination under low transmit power condition. To reduce the propagation errors between relays as well as the required transmit power during this data exchange, only the relay possessing the highest SNR is engaged into exchanging data by forwarding its received signal to the other relays. As for the remaining non-selected relays, i.e. with low SNR, the transmitted signal is estimated by using both signals received separately at different time slots (i.e., 1st and 2nd slot) from source and the 'best' selected relay, respectively, emulating virtual antenna array where appropriate weights for the antenna array are developed. In addition, we investigate distributed transmit beamforming and maximum ratio combining at the relays and the destination, respectively, to combine coherently the received signals. At the relay optimal location and for low SNR condition, the proposed method has significant better outage behavior and average throughput than conventional methods using one or two time slots for transmission.

In this work, a complete multiangulation system was developed and its performance in term of position estimation (PE) was determined. The developed system uses Bartlett's beam forming method to estimate AOA of the signal impinging on the 16-element sensor array in a uniform linear array (ULA) geometry at each ground receiving station (GRS). The AOA measurements are then used as input to a linear angulation algorithm for PE. The PE accuracy of the developed system was determined using Monte Carlo simulation and compared with the directional rotating antenna multiangulation system using a square GRS configuration. Simulation results shows that the developed multiangulation PE error is 50% lower than that of the directional rotating antenna system. Furthermore, the PE error of the developed system is higher for emitting sources within the system coverage with position bearings within 61 0 to 120 0 and 240 0 to 300 0 than other emitting source locations.

This paper presents an innovative design technique for feeding phase antenna arrays using CORPS (coherently radiating periodic structures) technology for reducing the number of phase shifters (PSs) in limited-scan applications with low side lobe level (SLL). The proposed configuration is implemented taking advantage of the phase interpolation property of a CORPS network of one layer. This configuration is built by interconnecting 2 × 3 CORPS networks in a strategic way in order to provide a reduction in the number of PSs while maintaining the scanning capability. Experimental results and full-wave simulations based in CST Microwave Studio reveal that the proposed design technique reduces the recombination losses and generates a better phase slope with respect to the basic CORPS network providing a reduction in the number of PSs. As a novel contribution the paper provides the full antenna system design in order to analyze and study the PSs reduction performance and scanning capabilities of the proposed technique to feed linear antenna arrays. The proposed design technique provides a reduction in the number of PSs for a scanning range of ±° in linear arrays. The array design model includes the application of the raised cosine amplitude distribution to generate a radiation pattern with minimum SLL. The linear array system was validated by experimental measurements of the full system prototype and full-wave simulations results are provided to verify the accuracy of the array model and to take mutual coupling into account. The proposed case provides a good design compromise with respect to other cases in the state-of-the-art.

This work presents a new topology of a Coherently Radiating Periodic Structure - Beam Forming Network (CORPS-BFN) and its application for multibeam systems. A unit cell, consisting of a transition from a coaxial input to an intersection of three strip-lines with an angular span of 120 degrees, is proposed and analysed. A periodical replication of the cell gives rise to a uniform layer, allowing a proper matching of the ports of the network. Stacked layers allow in-phase propagation and distribution of the energy through the structure, increasing the number of output ports with each layer.

For use as hydrophones, projectors and underwater microphones, there is always a need for calibrated sensors. Overview of multi path and effect of reflection on acoustic sound signals due to various objects is required prior to finding applications for different materials as sonar domes, etc. There is also a need to overview multi sensor array processing for many applications like finding direction of arrival and beam forming. Real time data acquisition is also a must for such applications.

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This document is unclassified. The information it contains is published subject to the conditions of the legend printed on the inside cover. Short quotations from it may be made in other publications if credit is for working copies for research purposes or for use in official NATO ^ the authorization of the Director of SACLANTCEN. ' given to the author(s). Except publications, reproduction requires This document is released to a NATO Government at the direction of the SACLANTCEN subject to the following conditions: 1. The recipient NATO Government agrees to use its best endeavours to ensure that the information herein disclosed, whether or not it bears a security classification, is not dealt with in any manner (a) contrary to the Intent of the provisions of the Charter of the Centre, or (b) prejudicial to the rights of the owner thereof to obtain patent, copyright, or other like statutory protection therefor. 2. If the technical information was originally released to the Centre by a NATO Government subject to restrictions clearly marked on this document the recipient NATO Government agrees to use its best endeavours to abide by the terms of the restrictions so imposed by the releasing Government.

Develop a new technology for processing wide bandwidth signals. This capability is important to the Navy for use in communications systems using high data rates, secure communications, RF signal processing, beamforming, and for handling complex signal environments in electromagnetic warfare. RESULTS Developed and demonstrated a fiber-optic finite impulse response (FIR) filter for processing 1-GHz bandwidth signals. The FIR filter was reconfigurable and could be adapted in realtime. This fiber-optic filter design with variable weights significantly increases the range of filtering operations possible for processing wide bandwidth signals. This type of FIR filter can be used to encode/decode wide bandwidth radar signals, to process spread spectrum signals, or to notch out agile jammers. Developed and demonstrated a differential amplifier for gigahertz bandwidth electrical signals using fiber optics and integrated optical devices. This device could be used as an integrated module in radar and communications systems. aI I-l.. .... ...

In this work, a complete multiangulation system was developed and its performance in term of position estimation (PE) was determined. The developed system uses Bartlett's beam forming method to estimate AOA of the signal impinging on the 16-element sensor array in a uniform linear array (ULA) geometry at each ground receiving station (GRS). The AOA measurements are then used as input to a linear angulation algorithm for PE. The PE accuracy of the developed system was determined using Monte Carlo simulation and compared with the directional rotating antenna multiangulation system using a square GRS configuration. Simulation results shows that the developed multiangulation PE error is 50% lower than that of the directional rotating antenna system. Furthermore, the PE error of the developed system is higher for emitting sources within the system coverage with position bearings within 61 0 to 120 0 and 240 0 to 300 0 than other emitting source locations.

25 SOUND AND VIBRATION/MARCH 2003 bands). It is also important to evaluate the difference between the sound intensity level and the sound pressure level. The descriptor measured in that case is called the PI index. The PI index is equivalent to the mean ...

We have described a method of obtaining useful information from noisy seismic refraction data. The simple method, tagged beam-forming technique, is based on the basic time-distance equations of refraction seismology. It involves basically of introducing relative time delays to individual seismic traces of seismic refraction spread to correct for the non-coincidence of the incidence seismic energy at different geophones, and averaging the traces to obtain the beam. The assumption here is that the signal is coherent between the geophones while the noise is random, and for groups of geophones corresponding to the same refraction segments of the travel time curve, this basic assumption is valid. The process of beam forming therefore leads to improvement in signal-to-noise ratio (SNR) and correct determination of the intercept times which are subsequently used to compute other geologic layer parameters. The ability of the applied technique to filter out or minimize random noise has been tested using a modified random number routine. The performance test on computation of geologic layer parameters using very noisy synthetic data reveals that the method is still very reliable even with very poor quality data having SNR as small as 0.05.

A simple technique to estimate the position of a given mobile source inside a building is based on the received signal strength. For this methodology to have a reasonable accuracy, radio visibility of the mobile by at least three access points is required. To reduce the number of the required access points and therefore simplify the underlying coverage design problem, we propose a novel scheme that takes into account the distribution of RF energy around the receiver. In other words, we assume that the receiver is equipped with a circular array antenna with beamforming capability. In this way, the spatial spectrum of the received power can be measured by electronically rotating the main lobe around the 360-degree field of view. This spatial spectrum can be used by a single receiver as a means for estimating the position of the mobile transmitter. In this paper, we investigate the feasibility of this methodology, and show the improvement achieved in the positioning accuracy.

Eigen-beamforming is capable of providing attractive performance gains in the context of multiple-input multiple-output systems, provided accurate channel state information (CSI) is available. However, when a realistic pilot-based channel predictor is used for acquiring the CSI, a significant performance degradation may be imposed by the phase-ambiguity inherent in the estimated eigenvectors. Sophisticated differentially encoded coded modulation (CM) schemes are amalgamated with the eigen-beamformer, when employing a minimum mean square error based pilot-assisted channel predictor for avoiding the performance degradation imposed by outdated channel estimation. It is shown that the amalgamated differentially encoded CM aided eigen-beamformer attained a coding gain of about 6.5 dB, when communicating over correlated Rayleigh fading channels.

We have described a method of obtaining useful information from noisy seismic refraction data. The simple method, tagged beam-forming technique, is based on the basic time-distance equations of refraction seismology. It involves basically of introducing relative time delays to individual seismic traces of seismic refraction spread to correct for the non-coincidence of the incidence seismic energy at different geophones, and averaging the traces to obtain the beam. The assumption here is that the signal is coherent between the geophones while the noise is random, and for groups of geophones corresponding to the same refraction segments of the travel time curve, this basic assumption is valid. The process of beam forming therefore leads to improvement in signal-to-noise ratio (SNR) and correct determination of the intercept times which are subsequently used to compute other geologic layer parameters. The ability of the applied technique to filter out or minimize random noise has been tested using a modified random number routine. The performance test on computation of geologic layer parameters using very noisy synthetic data reveals that the method is still very reliable even with very poor quality data having SNR as small as 0.05.

Beamforming using a microphone array mounted on the surface of a rigid or impedance sphere and cylinder is discussed. The introduction of a structure into the space occupied by or immediately adjacent to the array gives the array an effectively larger aperture and the possibility of enhanced performance. Additional improvements can be obtained through the introduction of a surface that permits air-coupled surface waves to propagate. Since surface waves travel at a speed less than the speed of sound in free space, the aperture of the array can be effectively further increased.

Beamforming using a microphone array mounted on the surface of a rigid or impedance sphere and cylinder is discussed. The introduction of a structure into the space occupied by or immediately adjacent to the array gives the array an effectively larger aperture and the possibility of enhanced performance. Additional improvements can be obtained through the introduction of a surface that permits air-coupled surface waves to propagate. Since surface waves travel at a speed less than the speed of sound in free space, the aperture of the array can be effectively further increased.

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In this work, a complete multiangulation system was developed and its performance in term of position estimation (PE) was determined. The developed system uses Bartlett's beam forming method to estimate AOA of the signal impinging on the 16-element sensor array in a uniform linear array (ULA) geometry at each ground receiving station (GRS). The AOA measurements are then used as input to a linear angulation algorithm for PE. The PE accuracy of the developed system was determined using Monte Carlo simulation and compared with the directional rotating antenna multiangulation system using a square GRS configuration. Simulation results shows that the developed multiangulation PE error is 50% lower than that of the directional rotating antenna system. Furthermore, the PE error of the developed system is higher for emitting sources within the system coverage with position bearings within 61 0 to 120 0 and 240 0 to 300 0 than other emitting source locations.

This paper introduces an original strategy to step up the capacity of ambient RF energy harvesters. The low rectification efficiency that comes from weak input power is enhanced through high gain antenna arrays that push the circuit to operate in a more efficient state. The prototype uses beam forming networks to build up a wide coverage since ambient energy can come from any direction, or the orientation of the rectenna may be unknown. By extending the operating range of rectifiers to higher input powers, the system operates as a very efficient narrow beam rectenna or as a synthetic high gain isotropic rectenna. The rectification efficiency pattern of one multi-beam rectenna, functioning in the 2.4 GHz band, is plotted and compared to a dipole rectenna's pattern. For a low incident power density of 4.10-5 mW.cm-2 , the rectification efficiency is largely improved in any direction : from 2.6% with a dipole rectenna up to 14%. Index Terms-Beam forming network (BSN), miniaturized Butler matrix, multiple beam antenna array, rectifier, high gain isotropic rectenna, efficiency pattern, RF energy harvesting.

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Automatic speech recognition (ASR) is difficult in environments such as multiparty meetings because of adverse acoustic conditions: background noise, reverberation and cross-talk. Microphone arrays can increase ASR accuracy dramatically in such situations. However, most existing beamforming techniques use time-domain signal processing theory and are based on a geometric analysis of the relationship between sources and microphones. This limits their application, and leads to performance degradation when the geometric properties are unavailable, or heterogeneous channels are used. We present a new posterior-based approach for microphone array speech recognition. Instead of enhancing speech signals, we enhance posterior phone probabilities which are used in a tandem ANN-HMM system. Significant improvements were achieved over a single channel baseline. Combining beamforming and our method is significantly better than beamforming alone, especially in a moving speakers scenario.

In this paper, an adaptive array antenna is implemented to enhance the performance of digital TV ISDB-T reception. Issues of realizing the proposed array antenna and its implementation by a joint hardware-software solution are also presented in this paper. Instead of using known reference signals, the proposed method utilizes the GI (Guard Interval) and a periodic property of OFDM signal as a constraint to realize MRC (Maximum Ratio Combining) and SMI (Sample Matrix Inversion) adaptive beam-forming algorithms. Experimental results show that the proposed system drastically improves the quality of reception. Moreover, the proposed system can achieve excellent performance under the conditions of strong interferences.

In this paper, we examine single user and multiuser multiple-input multiple-output (MIMO) beamforming networks with channel distribution information (CDI). Since CDI changes infrequently compared to channel state information (CSI), algorithms based on CDI can achieve significant savings in feedback compared to algorithms based on CSI. With CDI, we can only guarantee quality of service for a specified outage probability in the network. Assuming correlated Rayleigh fading on all the links, we derive a closed-form expression for the outage probability. Then, using this expression, we derive algorithms for joint transmit/receive beamforming and power control to minimize the weighted sum power in the network while guaranteeing these outage probabilities. For both single-user and multiuser MIMO scenarios, we present optimal algorithms under the Kronecker model assumption, and we present near-optimal algorithms assuming general correlation structures on the links. We then show that using these algorithms based on CDI, if we are willing to accept given outages on the links, we can achieve comparable power usage in the network relative to algorithms based on CSI.

Recently researchers were interested in hybrid algorithms for optimization problems for several communication systems. In this paper, a novel algorithm based on hybrid PSOGSA technique (combination of Gravitational Search Algorithm and Particle Swarm Optimization) is presented to enhance the performance analysis of beam-forming for smart antennas systems using N elements for Uniform Circular Array (UCA) geometry. Complex excitations (phases) of the array radiation pattern are optimized using hybrid PSOGSA technique for a set of simultaneously incident signals. Our results have shown tremendous improvement over the previous work was done using Uniform Linear Array (ULA) geometry and standard GSA in terms of normalized array factor and computational speed for normalized fitness values.

─ A review of current, past and projected activities in antenna development indicates a broad spectrum of requirements, and subsequently a variety of innovations to meet these requirements for military radar and communications systems. Designing the antennas in the operating environment, known as in-situ design, is an important factor in guaranteeing the successful operation of the antenna in the field. This paper presents the basic blocks in antenna development, followed by examples of some antennas developed at the Army Research Laboratory for military systems and applications. These include Rotman lenses as beam formers for electronically scanning arrays; phased arrays using MEMS phase shifters at 30 GHz; a 76-GHz narrow beam, low-sidelobe antenna for collision avoidance radar; and other specialized antennas. Of special interest is an effort on developing and using metamaterials in antenna designs, where practical realizations of such materials have the potential of improving the...

Applications for electronically steered arrays (ESA) in army communication systems span frequencies from UHF to Ka bands and requirements that include single and multiple beams, various scanning speeds, and different polarizations. The radiating apertures can be planar, conformal or segmented and distributed over multi-faceted structures. Examples include distributed apertures on military vehicles, antennas on elevated posts or towers on stationary or mobile platforms, and others. The beam former is an essential part of the ESA design and its optimization in functionality and cost lead to improving the whole system. This paper presents a concept for a distributed beam former that is composed of two stages: an RF stage with limited scanning steps and a digital stage that is capable of steering multiple beams in all required directions. The two-stage beam former uses fewer A/D converters than its all-digital counterpart and lower losses than the all-RF beam former. Examples are given for multi-faceted apertures.

In this paper, an adaptive array antenna is implemented to enhance the performance of digital TV ISDB-T reception. Issues of realizing the proposed array antenna and its implementation by a joint hardware-software solution are also presented in this paper. Instead of using known reference signals, the proposed method utilizes the GI (Guard Interval) and a periodic property of OFDM signal as a constraint to realize MRC (Maximum Ratio Combining) and SMI (Sample Matrix Inversion) adaptive beam-forming algorithms. Experimental results show that the proposed system drastically improves the quality of reception. Moreover, the proposed system can achieve excellent performance under the conditions of strong interferences.

This article presents reliable optimization techniques to improve the pulse generated by the Pulse Forming Networks (PFN) for high energy efficiency. The shape generated by PFN is not ideal however PFNs can be designed with better pulse performance by doing modifications and using techniques which can improve the desired output pulse shape and overall energy efficiency of the network. In this study, two novel techniques have been discussed. Particle Swarm Optimization (PSO) algorithm, proposed by Kennedy & Eberhart, a metaheuristic algorithm has been used to calculate the exact values of PFN with variable inductors which would tune PFN to generate the pulses with high energy efficiency. Green’s Function approach developed by Carl Neumann has been used to calculate the compensating voltage which can be used to compensate for the ripples, overshoot, rise time, fall time, etc. to improve the overall pulse performance. Using these optimization techniques, the energy efficiency of the ne...

We have described a method of obtaining useful information from noisy seismic refraction data. The simple method, tagged beam-forming technique, is based on the basic time-distance equations of refraction seismology. It involves basically of introducing relative time delays to individual seismic traces of seismic refraction spread to correct for the non-coincidence of the incidence seismic energy at different geophones, and averaging the traces to obtain the beam. The assumption here is that the signal is coherent between the geophones while the noise is random, and for groups of geophones corresponding to the same refraction segments of the travel time curve, this basic assumption is valid. The process of beam forming therefore leads to improvement in signal-to-noise ratio (SNR) and correct determination of the intercept times which are subsequently used to compute other geologic layer parameters. The ability of the applied technique to filter out or minimize random noise has been tested using a modified random number routine. The performance test on computation of geologic layer parameters using very noisy synthetic data reveals that the method is still very reliable even with very poor quality data having SNR as small as 0.05.

The Allen Telescope Array (ATA) is a Large-Number-Small-Diameter radio telescope array currently with 42 individual antennas and 5 independent back-end science systems (2 imaging FX correlators and 3 time domain beam formers) located at the Hat Creek Radio Observatory (HCRO). The goal of the ATA is to run multiple back-ends simultaneously, supporting multiple science projects commensally. The primary software control systems are based on a combination of Java, JRuby and Ruby on Rails. The primary control API is simplified to provide easy integration with new back-end systems while the lower layers of the software stack are handled by a master observing system. Scheduling observations for the ATA is based on finding a union between the science needs of multiple projects and automatically determining an efficient path to operating the various sub-components to meet those needs. When completed, the ATA is expected to be a world-class radio telescope, combining dedicated SETI projects with numerous radio astronomy science projects.

This work presents a novel eigen-beamforming technique suitable for tracking fading channels in multiple-input multiple-output (MIMO) systems employing low feedback rate, closed-loop feedback channels. The method uses a single unitary coordinate plane transformation to update the transmit antenna weights without requiring parameters that depend on fading rate, typically found in recursive methods. The computational complexity is fixed, in contrast with codebook solutions, whose operations count increases linearly with the codebook size. Simulations show that the new eigen-beamforming method reaches near optimal bit error probability performance in low mobility scenarios. Furthermore, by buffering the available feedback bits the proposed algorithm outperforms signed gradient methods for the same average feedback rate.

Recently researchers were interested in hybrid algorithms for optimization problems for several communication systems. In this paper, a novel algorithm based on hybrid PSOGSA technique (combination of Gravitational Search Algorithm and Particle Swarm Optimization) is presented to enhance the performance analysis of beam-forming for smart antennas systems using N elements for Uniform Circular Array (UCA) geometry. Complex excitations (phases) of the array radiation pattern are optimized using hybrid PSOGSA technique for a set of simultaneously incident signals. Our results have shown tremendous improvement over the previous work was done using Uniform Linear Array (ULA) geometry and standard GSA in terms of normalized array factor and computational speed for normalized fitness values.

A simple technique to estimate the position of a given mobile source inside a building is based on the received signal strength. For this methodology to have a reasonable accuracy, radio visibility of the mobile by at least three access points is required. To reduce the number of the required access points and therefore simplify the underlying coverage design problem, we propose a novel scheme that takes into account the distribution of RF energy around the receiver. In other words, we assume that the receiver is equipped with a circular array antenna with beamforming capability. In this way, the spatial spectrum of the received power can be measured by electronically rotating the main lobe around the 360-degree field of view. This spatial spectrum can be used by a single receiver as a means for estimating the position of the mobile transmitter. In this paper, we investigate the feasibility of this methodology, and show the improvement achieved in the positioning accuracy.

Collaborative beamforming (CB) is a power efficient method for data communications in wireless sensor networks (WSNs) which aims at increasing the transmission range in the network by radiating the power from a cluster of sensor nodes in the directions of the intended base station(s) or access point(s) (BSs/APs). The CB average beampattern expresses a deterministic behavior and can be used for characterizing/controling the transmission at intended direction(s), since the mainlobe of the CB beampattern is independent on the particular random node locations. However, the CB for a cluster formed by a limited number of collaborative nodes results in a sample beampattern with sidelobes that severely depend on the particular node locations. High level sidelobes can cause unacceptable interference when they occur at directions of unintended BSs/APs. Therefore, sidelobe control in CB has a potential to increase the network capacity and wireless channel availability by decreasing the interference. Traditional sidelobe control techniques are proposed for centralized antenna arrays and, therefore, are not suitable for WSNs. In this paper, we show that distributed, scalable, and low-complexity sidelobe control techniques suitable for CB in WSNs can be developed based on node selection technique which make use of the randomness of the node locations. A node selection algorithm with low-rate feedback is developed to search over different node combinations. The performance of the proposed algorithm is analyzed in terms of the average number of trials required to select the collaborative nodes and the resulting interference. Our simulation results approve the theoretical analysis and show that the interference is significantly reduced when node selection is used with CB.

Conventional multibeam satellite communications systems ensure coverage of wide areas through multiple fixed beams where all users inside a beam share the same bandwidth. The authors consider a new and more flexible system where each user is assigned his own beam, and the users can be very geographically dispersed. This is achieved through the use of a large direct radiating array coupled with adaptive beamforming so as to reject interferences and to provide a maximal gain to the user of interest. New fast-converging adaptive beamforming algorithms are presented, which allow one to obtain good signal to interference and noise ratio with a number of snapshots much lower than the number of antennas in the array. These beamformers are evaluated on reference scenarios.

In an earlier publication we demonstrated that by using pairs of pulses of different colors (e.g., red and blue) it is possible to excite a dilute ensemble of molecules such that lasing and/or gain-swept superradiance is realized in a direction toward the observer. This approach is a conceptual step toward spectroscopic probing at a distance, also known as standoff spectroscopy. In the present paper, we propose a related but simpler approach on the basis of the backward-directed lasing in optically excited dominant constituents of plain air, N 2 and O 2 . This technique relies on the remote generation of a weakly ionized plasma channel through filamentation of an ultraintense femtosecond laser pulse. Subsequent application of an energetic nanosecond pulse or series of pulses boosts the plasma density in the seed channel via avalanche ionization. Depending on the spectral and temporal content of the driving pulses, a transient population inversion is established in either nitrogen- o...

In an earlier publication we demonstrated that by using pairs of pulses of different colors (e.g., red and blue) it is possible to excite a dilute ensemble of molecules such that lasing and/or gain-swept superradiance is realized in a direction toward the observer. This approach is a conceptual step toward spectroscopic probing at a distance, also known as standoff spectroscopy. In the present paper, we propose a related but simpler approach on the basis of the backward-directed lasing in optically excited dominant constituents of plain air, N 2 and O 2 . This technique relies on the remote generation of a weakly ionized plasma channel through filamentation of an ultraintense femtosecond laser pulse. Subsequent application of an energetic nanosecond pulse or series of pulses boosts the plasma density in the seed channel via avalanche ionization. Depending on the spectral and temporal content of the driving pulses, a transient population inversion is established in either nitrogen- o...

In this work, a complete multiangulation system was developed and its performance in term of position estimation (PE) was determined. The developed system uses Bartlett’s beam forming method to estimate AOA of the signal impinging on the 16-element sensor array in a uniform linear array (ULA) geometry at each ground receiving station (GRS). The AOA measurements are then used as input to a linear angulation algorithm for PE. The PE accuracy of the developed system was determined using Monte Carlo simulation and compared with the directional rotating antenna multiangulation system using a square GRS configuration. Simulation results shows that the developed multiangulation PE error is 50% lower than that of the directional rotating antenna system. Furthermore, the PE error of the developed system is higher for emitting sources within the system coverage with position bearings within 61 0 to 120 0 and 240 0 to 300 0 than other emitting source locations. Keywords: multiangulation system...

This paper deals with an efficient receiver for applications in direct sequence-code-division multiple access wireless communication systems. This receiver combines a modified scheme of a parallel interference cancellation detector with antenna arrays with optimum beamforming and is used at the base station for the detection of asynchronous user signals. Each user's transmission channel is assumed to be a multipath frequency-selective independent Rayleigh fading channel. The receiver operates by dividing the signals into reliable and unreliable sets following space-time combining. The reliable signals are detected and canceled from the whole signal received at each sensor. Unreliable signals are then detected to improve the decision reliability. The receiver performance in terms of bit-error probability is analytically derived and optimized. According to the analytical and simulation results, this receiver outperforms previously proposed schemes and, thanks to its low implementation complexity, real-time operation is achieved.